WebGPURenderer: Use renderBundles for repeated mipmap creation.

[aardgoose]

The example webgpu_backdrop_area requires regeneration of a texture mipmap for each frame, using bundles allows the overhead to be reduced.

The renderBundles are only cached when a texture is mipmapped more than once.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
685.4 kB (169.7 kB)	685.4 kB (169.7 kB)	+0 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

Filesize dev	Filesize PR	Diff
462 kB (111.4 kB)	462 kB (111.4 kB)	+0 B

[RenaudRohlinger]

@aardgoose After I saw this PR I was wondering, since WebGPU doesn't have a multidraw API like WebGL as RenderBundles are basically the same thing, could we update the BatchedMesh part of the WebGPUBackend with renderBundle?

So that this part would be bundled OOTB:

if ( object.isBatchedMesh === true ) {

	const starts = object._multiDrawStarts;
	const counts = object._multiDrawCounts;
	const drawCount = object._multiDrawCount;
	const drawInstances = object._multiDrawInstances;

	const bytesPerElement = hasIndex ? index.array.BYTES_PER_ELEMENT : 1;

	for ( let i = 0; i < drawCount; i ++ ) {

		const count = drawInstances ? drawInstances[ i ] : 1;
		const firstInstance = count > 1 ? 0 : i;

		passEncoderGPU.drawIndexed( counts[ i ], count, starts[ i ] / bytesPerElement, 0, firstInstance );

	}

}

[aardgoose]

I'm not sure it is worth it yet, I looked at the chromium/dawn issue log and it appears the multidraw has been implemented in Dawn for D3D12 and Vulkan backends, but not Metal yet. So it looks like it will appear in Chrome, although when is not know of course.

Although could you take it one step further and use multiple drawIndirect() with the a single indirect buffer mapped at different offsets at for each call, so you could try gpu compute directed rendering? That way you could get more of the benefits of multidraw and make it more worthwhile?

[RenaudRohlinger]

I like the idea a lot. I guess it's time to work on [WebGPU] drawIndirect and drawIndexedIndirect ^^.